Method of manufacturing a semiconductor device and a process of a thin film transistor

ABSTRACT

To enable radiating an optimum energy beam depending upon the structure of a substrate (whether a metallic film is formed or not) when an amorphous semiconductor film is crystallized and uniformly crystallizing the overall film, first, a photoresist film and the area of an N −  doped amorphous silicon film on the photoresist film are selectively removed by a lift-off method. Hereby, the amorphous silicon film is thicker in an area except an area over a metallic film (a gate electrode) than in the area over the metallic film In this state, a laser beam is radiated. The N −  doped amorphous silicon film and an amorphous silicon film are melted by radiating a laser beam and afterward, melted areas are crystallized by cooling them to room temperature. As the amorphous silicon film is thicker in the area except the area under which the metallic film (the gate electrode) is formed than in the area under which the metallic film is formed, the maximum temperature of the surface of the film is equal and the overall film can be uniformly crystallized.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method of manufacturing asemiconductor device in which a film is formed by crystallizing asemiconductor film by radiating an energy beam on the semiconductor filmsuch as amorphous silicon, particularly relates to a method ofmanufacturing a semiconductor device provided with structure in whichthe substrate material of a semiconductor film to be crystallized is noteven such as a thin film transistor (TFT) used for a liquid crystaldisplay (LCD) and others.

[0003] 2. Description of the Related Art

[0004] A TFT liquid crystal display uses a thin film transistor (TFT)for a pixel provided with a switching function and this TFT is formed ona glass substrate corresponding to each pixel of the liquid crystaldisplay. There are two types of TFTs of TFT consisting of amorphoussilicon films and TFT consisting of polycrystalline silicon films, andhigh-performance TFT consisting of polycrystalline silicon films ofthese can be produced on a glass substrate at low temperature byirradiating an amorphous silicon film with an energy beam, particularlyan excimer laser beam. The peripheral circuit of a liquid crystaldisplay and a pixel switching device can be produced on the samesubstrate by using such TFT consisting of polycrystalline silicon films.Recently, TFT provided with bottom gate structure attracts attention ofTFTs consisting of polycrystalline silicon films because particularly,stable characteristics can be obtained.

[0005] This TFT provided with bottom gate structure is constituted asshown in FIG. 9 for example. That is, a gate electrode 101 consisting ofmolybdenum tantalum (MoTa) is formed on a glass substrate 100 and anoxide film (Ta₂O₅) 102 is formed on this gate electrode 101. A gateinsulating film consisting of a silicon nitride (SiN_(x)) film 103 and asilicon dioxide (SiO₂) film 104 is formed on the glass substrate 100including this oxide film 102 and further, a thin polycrystallinesilicon film 105 is formed on this silicon dioxide film 104. A sourcearea 105 a and a drain area 105 b are respectively formed by dopingN-type impurities for example in this polycrystalline silicon film 105.A silicon dioxide film (SiO₂) 106 is selectively formed corresponding tothe channel area 105 c of this polycrystalline silicon film 105 on thepolycrystalline silicon film 105. An N⁺ doped polycrystalline siliconfilm 107 is formed on the polycrystalline silicon film 105 and thesilicon dioxide film 106 and further, a source electrode 108 and a drainelectrode 109 are respectively formed opposite to the source area 105 aand the drain area 105 b on this N⁺ doped polycrystalline silicon film107.

[0006] This TFT provided with bottom gate structure can be manufacturedby the following method: That is, after a molybdenum tantalum (MoTa)film is formed on an overall glass substrate 100, a gate electrode 101is formed by patterning this molybdenum tantalum film by etching so thatthe film is in a predetermined shape. Afterward, an oxide film 102 isformed on the surface of the gate electrode 101 by anodizing the gateelectrode 101. Next, a silicon nitride film 103, a silicon dioxide film104 and an amorphous silicon film are sequentially formed on the overalloxide film 102 by plasma enhanced chemical vapor deposition (PECVD).

[0007] Next, this amorphous silicon film is once fused by irradiatingthis amorphous silicon film with a laser beam by an excimer laser forexample and afterward, crystallized by cooling the film to roomtemperature. Hereby, the amorphous silicon film is changed to apolycrystalline silicon film 105. Next, after a silicon dioxide film 106in the shape corresponding to a channel area is selectively formed onthe polycrystalline silicon film 105 of a part to be a channel area, anamorphous silicon film including N-type impurities, for examplephosphorus (P) and arsenic (As) is formed and changed to an N⁺ dopedpolycrystalline silicon film 107 by irradiating the above amorphoussilicon film with a laser beam by an excimer laser again, and theimpurities are electrically activated.

[0008] Next, after an aluminum (Al) film is formed on the overall filmby a sputtering method using argon (Ar) as sputtering gas, this aluminumfilm and the N⁺ doped polycrystalline silicon film 107 are respectivelypatterned by etching so that they are in a predetermined shape, and asource electrode 108 and a drain electrode 109 are respectively formedon a source area 105 a and a drain area 105 b. Next, dangling bond andothers are inactivated by exposing the above silicon dioxide film tohydrogen and hydrogenating a channel area 105 c by a hydrogen radicaland atomic hydrogen which both pass through the silicon dioxide film106. TFT provided with bottom gate structure shown in FIG. 9 can beobtained by the above process.

OBJECT AND SUMMARY OF THE INVENTION

[0009] As described above, in the prior method, an energy beam isradiated onto an amorphous silicon film in a process for crystallizingit, however, at this time, the structure of a substrate under theamorphous silicon film is not even. That is, a metallic film (the gateelectrode 101) is applied on the glass substrate 100, the substrateunder the amorphous silicon film consists of metal and glass which aredifferent in material and heretofore, an energy beam is simultaneouslyradiated onto an amorphous silicon film over the respective substrateand film. In this case, the same energy beam as the following energy isalso radiated onto an amorphous silicon film over the glass substrate100 based upon the optimum condition of the crystallizing energy of theamorphous silicon film in a channel area over the metallic film (thegate electrode 101).

[0010] However, even if the same amorphous silicon film is used, theoptimum value of energy required for crystallization is differentdepending upon whether a substrate is made of metal or glass becausethermal conductivity is different. Therefore, more energy beam isradiated onto the amorphous silicon film on the glass substrate 100 bythe prior method according to the optimum condition of the amorphoussilicon film on the metallic film (the gate electrode 101) than theoptimum condition and therefore, there is a problem that partially afilm is broken.

[0011] The present invention is made to solve such problems and theobject is to provide a method of manufacturing a semiconductor device inwhich an optimum quantity of energy beams can be radiated depending uponthe structure of a substrate when an amorphous semiconductor film iscrystallized, an overall film can be uniformly crystallized and a filmis never broken.

[0012] A method of manufacturing a semiconductor device according to thepresent invention comprises a process for selectively forming a metallicfilm on a substrate, a process for forming an amorphous semiconductorfilm on the substrate and the metallic film so that an area on thesubstrate is thicker than an area on the metallic film and a process foruniformly polycrystallizing the semiconductor film by radiating anenergy beam onto the semiconductor film.

[0013] More concretely, a method of manufacturing a semiconductor deviceaccording to the present invention comprises a process for forming ametallic film as the gate electrode of a thin film transistor on thesurface of a substrate and forming an insulating film on this metallicfilm and the substrate, a process for forming a first amorphoussemiconductor film the thickness of which is uniform on the insulatingfilm, a process for selectively forming a lift-off film in an area onthe first semiconductor film corresponding to the metallic film, aprocess for forming a second amorphous semiconductor film the thicknessof which is uniform including impurities on the lift-off film and thefirst semiconductor film and a process for polycrystallizing the firstand second semiconductor films by radiating an energy beam after thelift-off film and an area on the lift-off film of the secondsemiconductor film are selectively removed and respectively forming thesource area and the drain area of the thin film transistor.

[0014] A method of manufacturing a semiconductor device according to thepresent invention may be also constituted so that it comprises a processfor forming a metallic film as the gate electrode of a thin filmtransistor on the surface of a substrate and forming an insulating filmon this metallic film and the substrate, a process for selectivelyforming a lift-off film in an area on the insulating film correspondingto the metallic film, a process for forming a first amorphoussemiconductor film the thickness of which is uniform includingimpurities on the lift-off film and the insulating film, a process forforming a second amorphous semiconductor film the thickness of which isuniform on the insulating film and the first semiconductor film afterthe lift-off film and an area on the lift-off film of the firstsemiconductor film are selectively removed and a process forpolycrystallizing the first and second semiconductor films by radiatingan energy beam after the second semiconductor film is formed andrespectively forming the source area and the drain area of the thin filmtransistor.

[0015] According to a method of manufacturing a semiconductor deviceaccording to the present invention, as the thickness of a semiconductorfilm is different depending upon the state of a substrate (whether ametallic film is formed or not) when an energy beam is radiated tocrystallize an amorphous semiconductor film, the overall semiconductorfilm can be uniformly crystallized by radiating beams with the sameenergy.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIGS. 1 A to C are sectional views showing a method ofmanufacturing a thin film transistor equivalent to a first embodimentaccording to the present invention every process;

[0017]FIGS. 2A and 2B are sectional views showing a process next to FIG.1;

[0018]FIGS. 3A to-3D are sectional views showing a method ofmanufacturing a thin film transistor equivalent to a second embodimentaccording to the present invention every process;

[0019]FIGS. 4A and 4B explain the basic principle of the presentinvention, FIG. 4A is a sectional view showing structure in which ametallic film is formed under a silicon film and FIG. 4B is a sectionalview showing structure in which a metallic film is not formed under asilicon film;

[0020]FIG. 5 shows parameters of each material used for simulation forexplaining the principle shown in FIGS. 4;

[0021]FIG. 6 is a drawing showing a characteristic for explaining thechange of the temperature of a silicon film when a laser beam isradiated on the structure shown in FIG. 4A;

[0022]FIG. 7 is a drawing showing a characteristic for explaining thechange of the temperature of a silicon film when a laser beam isradiated on the structure shown in FIG. 4B;

[0023]FIG. 8 is a drawing showing a characteristic showing the thicknessof a silicon film in the structure shown in FIG. 4B to the thickness (30nm) of an insulating film shown in FIG. 4A for obtaining the maximumtemperature of 2650 K in both structures shown in FIGS. 4A and 4B; and

[0024]FIG. 9 is a sectional view for explaining the prior structure of athin film transistor and the manufacturing method.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Referring to drawings, embodiments according to the presentinvention will be described in detail below.

[0026] Prior to the concrete description of the embodiments, first, thebasic principle of the present invention will be described. As describedabove, even if the same amorphous silicon film is used, the optimumvalue of energy required for crystallization is different depending uponwhether a substrate is made by metal or glass. According to the presentinvention, an overall semiconductor film can be uniformly crystallizedby radiating beams with the same energy by changing the thickness of theamorphous silicon film depending upon the structure of a substrate(whether a metallic film is formed or not). The reasons will bedescribed below.

[0027]FIGS. 4A and 4B show examples of substrates which are different inthe substrate structure of a silicon film. The structure shown in FIG.4A is formed by sequentially forming a nickel (Ni) film 41 on a glasssubstrate 40, a silicon nitride (SiN) film 42, an insulating film (SiO₂)43 and an amorphous silicon film (a-Si) 44 on the nickel film. In themeantime, the structure shown in FIG. 4B is formed by sequentiallyforming a silicon nitride (SiN) film 42 on a glass substrate 40, aninsulating film (SiO₂) 43 and an amorphous silicon film 44 and is thesame as the structure shown in FIG. 4A except that a metallic film (thenickel film 41) is not formed under the amorphous silicon film 44.

[0028]FIG. 6 shows the result of simulating the change of thetemperature of the surface of the amorphous silicon film 44 when anexcimer laser beam (energy: 360 mJ/cm², pulse length: 30 ns, wavelength:308 nm) is radiated onto the amorphous silicon film 44 in the structureshown in FIG. 4A as an energy beam. In the meantime, FIG. 7 shows theresult of simulating the change of the temperature of the surface of theamorphous silicon film 44 when the same excimer laser beam is radiatedonto the amorphous silicon film 44 in the structure shown in FIG. 4B.FIG. 5 shows the parameters of the material of each film.

[0029] As clear from the result of FIGS. 6 and 7, while an excimer laserbeam is radiated, the temperature of the amorphous silicon film 44rapidly rises to a melting point (the melting point of a-Si) and whenthe temperature reaches the melting point, the incline of rising is oncegentle because of the latent heat of melting and afterward, thetemperature rapidly rises again. Even if excimer laser beams with thesame energy are radiated, the maximum temperature is different dependingupon the substrate structure of the amorphous silicon film 44. That is,if a metallic film (the nickel film 41) is formed below the amorphoussilicon film 44 as shown in FIG. 4A, the maximum temperature isapproximately 2650 (K), while if a metallic film (the nickel film 41) isnot formed below the amorphous silicon film as shown in FIG. 4B, themaximum temperature is approximately 2940 (K) and is greatly differentdepending upon the structure of a substrate. The difference between themaximum temperatures is increased as the insulating film 43 is thinned.When the radiation of an excimer laser beam is finished after thetemperature reaches the maximum temperature, heat is transmitted in thedirection of the glass substrate 40 and the temperature of the amorphoussilicon film 44 gradually falls in both structures shown in FIGS. 4 Aand B. When the temperature reaches temperature required forcrystallizing silicon (1410° C.) , latent heat is generated bycrystallization, the temperature is held fixed for some time(crystallizing time) and afterward, gradually falls again.

[0030] If an excimer laser beam is radiated onto the amorphous siliconfilm 44 in the respective structures shown in FIGS. 4 A and B, it isdesirable so as to optimize a laser beam condition that the maximumtemperature which can be achieved by the same energy of the surface ofeach amorphous silicon film 44 is the same. The inventors of the presentinvention consider that if a silicon film on a metallic film (the nickelfilm 41) is thickened in the structure shown in FIG. 4B, the sametemperature condition as in the structure shown in FIG. 4A can be setand therefore, the temperature of the surface of the silicon film can beequal independent of the structure of a substrate (whether a metallicfilm is formed or not), and obtain a drawing showing a characteristic inFIG. 8 in experiments.

[0031]FIG. 8 shows the thickness of the silicon film 44 in the structureshown in FIG. 4B to that of the silicon film 44 which is 30 nm shown inFIG. 4A for obtaining the maximum temperature of 2650 K in bothstructures shown in FIGS. 4 A and B. That is, FIG. 8 shows the result ofsimulating the thickness of the silicon film 44 in the structure shownin FIG. 4B in case that in the structure shown in FIG. 4A, the thicknessof the silicon film 44 on the nickel (Ni) film 41 is set to 30 nm, thethickness of the nickel film 41 is set to 100 nm, the thickness of thesilicon nitride (SiN) film 42 is set to 50 nm and the thickness of aninsulating film (SiO₂) 43 is changed so that the temperature of thesurface of the silicon film in the structures shown in FIGS. 4 A and Breaches 2650 K (the boiling point of silicon). This result shows thatwhen the thickness of the insulating film 43 in the structure shown inFIG. 4A is reduced, the silicon film is required to be thickened in thestructure shown in FIG. 4B to obtain the same maximum temperature. Thatis, the result shows that the thickness of the silicon film in thestructure shown in FIG. 4B has only to be set according to the resultshown in FIG. 8 so that the maximum temperature of the surface of thesilicon film 44 obtained by radiating an energy beam in the structuresshown in FIGS. 4 A and B can be equal so as to optimize a laser beamcondition.

[0032] The present invention utilizes such a result for uniformlycrystallizing an overall film at the same maximum temperature bychanging the thickness of a silicon film depending upon the structure ofa substrate (whether a metallic film is formed or not) on the samesubstrate. An example in which the present invention is applied to amethod of manufacturing a thin film transistor will be described below.

[0033] First Embodiment

[0034]FIGS. 1 A to C and FIGS. 2 A and B show a method of manufacturinga thin film transistor equivalent to a first embodiment of the presentinvention in the order of processes. First, as shown in FIG. 1A, a gateelectrode 11 consisting of a nickel (Ni) film the thickness of which is100 nm is formed on the overall surface of a substrate, for example aglass substrate 10 by sputtering using argon (Ar) as sputtering gas.Next, a laminated insulting film 12 is formed by sequentially forming asilicon nitride (SiN_(x)) layer which is 50 nm thick and a silicondioxide (SiO₂) layer which is 100 nm thick on the overall surfacesimilarly by sputtering using helium (He) as sputtering gas, and next,an amorphous silicon film 13 which is 30 nm thick is formed on theinsulating film 12 by PECVD for example.

[0035] After the amorphous silicon film 13 is formed, a photoresist isapplied onto this amorphous silicon film 13 and exposure (back exposure)15 to this photoresist by gamma rays (wavelength: 436 nm) for example isexecuted from the rear side of the glass substrate 10. At this time, aphotoresist film 14 with the same width as the gate electrode 12 asshown in FIG. 1B is formed by self-matching with the gate electrode 12functioning as a mask. Next, as shown in FIG. 1C, an N⁺ doped amorphoussilicon film 16 including N-type impurities, for example phosphorus (P)is formed on the insulating film 12 and the photoresist film 14 by PECVDfor example. The temperature of the substrate at this time shall be theheat-resistant temperature (for example, 150° C.) of the photoresist orless. The thickness of the N⁺ doped amorphous silicon film 16 isdetermined according to the result shown in FIG. 8 based upon thethickness of the SiO₂ layer of the insulating film 12. As the thicknessof the SiO₂ layer of the insulating film 12 is set to 100 nm in thisembodiment, the required thickness of the amorphous silicon film in anarea except the gate electrode 11 is 48 nm as shown in FIG. 8.Therefore, the thickness of the N⁺ doped amorphous silicon film 16 isset to 18 nm obtained by subtracting 30 nm (the thickness of theamorphous silicon film 13) from 48 nm.

[0036] Afterward, as shown in FIG. 2A, the photoresist film 14 and thearea of the N⁺ doped amorphous silicon film 16 on the photoresist film14 (that is, an area corresponding to a channel area) are selectivelyremoved by a lift-off method. Hereby, the amorphous silicon film isthicker in an area except an area over metal (the gate electrode 11)than in the area over the metal. In this state, next, a laser beam 17 isradiated from the surface of the substrate. The N⁺ doped amorphoussilicon film 16 and the amorphous silicon film 13 are melted byradiating a laser beam 17 as described above and afterward, melted areasare crystallized by cooling them to room temperature. At this time, theN-type impurities in the N⁺ doped amorphous silicon film 16 are diffusedon the side of the amorphous silicon film 13 and an N⁺ dopedpolycrystalline silicon film 18 provided with a source area 18 a and adrain area 18 b is formed. As in this embodiment, the amorphous siliconfilm is thicker in the area except the area over the metallic film (thethickness of the amorphous silicon film: 48 nm) than in the area overthe metallic film (the gate electrode 11) (thickness: 30 nm), themaximum temperature of the surface of the film is substantially equal asdescribed above and the overall film can be uniformly crystallized.

[0037] It is desirable for a laser beam 17 that a laser beam thewavelength of which the N⁺ doped amorphous silicon film 18 can absorb,particularly a pulse laser beam by an excimer laser is used. In detail,a pulse laser beam (wavelength: 308 nm) by XeCl excimer laser, a pulselaser beam (wavelength: 350 nm) by XeF excimer laser and others areused.

[0038] Next, as shown in FIG. 2B, electrodes 19 a and 19 b consisting ofaluminum (Al) are respectively formed on the source area 18 a and thedrain area 18 b in the N⁺ doped polycrystalline silicon film 18 bysputtering using argon (Ar) as sputtering gas. Next, the channel area 18c in the N⁺ doped polycrystalline silicon film 18 is hydrogenated inhydrogen plasma to inactivate dangling bond and others.

[0039] As described above, according to the method of manufacturing athin film transistor equivalent to this embodiment, as the thickness ofa silicon film is set to a different value depending upon the structureof a substrate (whether a metallic film is formed or not) when a laserbeam 17 is radiated for crystallization, the silicon film can beuniformly crystallized over the overall substrate. Therefore, a film isnever broken and a process margin can be increased.

[0040] Second Embodiment

[0041]FIGS. 3A to 3D show a method of manufacturing a thin filmtransistor equivalent to a second embodiment of the present invention inthe order of processes. In this embodiment, the order in the firstembodiment of forming an amorphous silicon film and a doped amorphoussilicon film is inverted.

[0042] That is, first as shown in FIG. 3A, a gate electrode 31consisting of a nickel (Ni) film which is 100 nm thick is formed on theoverall surface of a substrate, for example a glass substrate 30 bysputtering using argon (Ar) as sputtering gas. Next, a laminatedinsulating film 32 which is 100 nm thick is formed by sequentiallyforming a silicon nitride (SiN_(x)) film and a silicon dioxide (SiO₂)film on the overall substrate similarly by sputtering using helium (He)as sputtering gas and next, a photoresist is applied onto thisinsulating film 32 and exposure (back exposure) 35 to this photoresistby gamma rays (wavelength: 436 nm) for example is executed from the rearside of the glass substrate 30. At this time, a photoresist film 33 withthe same width as the gate electrode 31 is formed by self-matching withthe gate electrode 31 functioning as a mask. Next, an N⁺ doped amorphoussilicon film 34 including N-type impurities, for example phosphorus (P)is formed on the insulating film 32 and the photoresist film 33 by PECVDfor example. The temperature of the substrate at this time shall be theheat-resistant temperature (for example, 150° C.) of the photoresist orless. The thickness of this N⁺ doped amorphous silicon film 34 isdetermined according to a drawing showing a characteristic shown in FIG.8 based upon the thickness of the insulating film 32 as in the firstembodiment. That is, as the thickness of the SiO₂ layer of theinsulating film 32 is set to 100 nm in this embodiment, the requiredthickness of the amorphous silicon film in an area except the gateelectrode 31 is 48 nm as shown in FIG. 8. Therefore, the thickness ofthe N⁺ doped amorphous silicon film 34 is set to 18 nm obtained bysubtracting 30 nm (the thickness of an amorphous silicon film 36 to beformed continuously) from 48 nm.

[0043] Afterward, as shown in FIG. 3B, the photoresist film 33 and thearea of the N⁺ doped amorphous silicon film 34 on the photoresist film33 (that is, an area corresponding to a channel area) are selectivelyremoved by a lift-off method.

[0044] Next, as shown in FIG. 3C, an amorphous silicon film 36 which is30 nm thick is formed on the N⁺ doped amorphous silicon film 34 and theinsulating film 32 by PECVD for example. Hereby, the amorphous siliconfilm is thicker in an area (the thickness of the amorphous silicon film:48 nm) except an area over metal (the gate electrode 31) than in thearea (thickness: 30 nm) over metal. In this state, next, a laser beam 37is radiated on the overall surface from the surface of the substrate.The N⁺ doped amorphous silicon film 34 and the amorphous silicon film 36are melted by radiating a laser beam 17 as described above andafterward, melted areas are crystallized by cooling them to roomtemperature. At this time, the N-type impurities in the N⁺ dopedamorphous silicon film 34 are diffused on the side of the amorphoussilicon film 36 and an N⁺ doped polycrystalline silicon film 38 providedwith a source area 38 a and a drain area 38 b is formed. As in thisembodiment, the amorphous silicon film is also thicker in the area (thethickness of the amorphous silicon film: 48 nm) except the area over themetallic film than in the area (thickness: 30 nm) over the metallic film(the gate electrode 31), the maximum temperature of the surface of thefilm is substantially equal and the overall film can be uniformlycrystallized.

[0045] Next, as shown in FIG. 3D, electrodes 39 a and 39 b consisting ofaluminum (Al) are respectively formed on the source area 38 a and thedrain area 38 b in the N⁺ doped polycrystalline silicon film 38 bysputtering using argon (Ar) as sputtering gas. Next, a channel area 38 cin the N⁺ doped polycrystalline silicon film 38 is hydrogenated inhydrogen plasma to inactivate dangling bond and others.

[0046] As described above, according to the method of manufacturing athin film transistor equivalent to this embodiment, as the thickness ofa silicon film is set to a different value depending upon the state of asubstrate (whether a metallic film is formed or not) when a laser beam37 is radiated for crystallization, the silicon film can be uniformlycrystallized over the overall substrate and a film can be prevented frombeing broken.

[0047] The embodiments according to the present invention are describedabove, however, the present invention is not limited to the aboveembodiments and may be variously transformed. For example, in the aboveembodiments, a metallic film under a silicon film is a nickel film,however, it may be also formed by the other metallic film. In the aboveembodiments, a silicon film is used for an amorphous semiconductor film,however, the other amorphous film may be also used if only it can becrystallized by radiating an energy beam. Further, in the aboveembodiments, the present invention is applied to a method ofmanufacturing a thin film transistor, however, it may be also applied toa process for manufacturing the other semiconductor device. A method offorming amorphous semiconductor films different in thickness dependingupon the structure of a substrate is not limited to the methodsdescribed in the above embodiments and the other method may be alsoused.

[0048] As described above, according to the methods of manufacturing asemiconductor device according to the present invention, as thethickness of a semiconductor film is set to a different value dependingupon the state of a substrate (whether a metallic film is formed or not)when an energy beam is radiated to crystallize the amorphoussemiconductor film, the overall semiconductor film can be uniformlycrystallized by radiating beams with the same energy. Therefore, thereis effect that a film is never broken and a process margin can beincreased.

What is claimed is:
 1. A method of manufacturing a semiconductor device,comprising: a process for selectively forming a metallic film on asubstrate; a process for forming a semiconductor film over saidsubstrate and metallic film; and a process for crystallizing saidsemiconductor film by radiating an energy beam on said semiconductorfilm in a state in which said semiconductor film is thicker in an areaover said substrate than in an area over said metallic film.
 2. A methodof manufacturing a semiconductor device according to claim 1, wherein:said semiconductor film is an amorphous semiconductor film.
 3. A methodof manufacturing a semiconductor device according to claim 1, wherein:said semiconductor film is a silicon film.
 4. A method of manufacturinga semiconductor device according to claim 1, wherein: said semiconductorfilm is an amorphous silicon film.
 5. A method of manufacturing asemiconductor device according to claim 1, wherein: said energy beam isan excimer laser beam.
 6. A method of manufacturing a semiconductordevice according to claim 1, wherein: the thickness of saidsemiconductor film in the area over said substrate and that in the areaover said metallic film are selected in said process forpolycrystallizing said semiconductor film by radiating said energy beamso that the maximum temperature in the respective areas of saidsemiconductor film is substantially equal.
 7. A method of manufacturinga semiconductor device according to claim 1, wherein: a process forforming an insulating film on said substrate and said metallic film isincluded before said process for forming said semiconductor film andafter said process for forming said metallic film.
 8. A method ofmanufacturing a semiconductor device according to claim 7, wherein: thethickness of said insulating film, that in the area over said substrateof said semiconductor film and that in the area over said metallic filmof said semiconductor film are selected in said process forpolycrystallizing said semiconductor film by radiating said energy beamso that the maximum temperature in the respective areas of saidsemiconductor film is substantially equal.
 9. A process of manufacturinga thin film transistor; comprising: a process for forming a gateelectrode on a part of a substrate wherein said gate electrode is ametallic film; a process for forming an insulating film on saidsubstrate and said gate electrode; a process for forming a firstsemiconductor film with a uniform thickness on said insulating film; aprocess for forming a lift-off film in an area corresponding to saidgate electrode on said first semiconductor film wherein said lift-offfilm is a photoresist; a process for forming a second semiconductor filmwith uniform thickness on said lift-off film and said firstsemiconductor film wherein said thickness is determined based on amaterial of said substrate; a process for removing said lift-off filmand said second semiconductor film on said lift-off film; a process foruniformly crystallizing said first semiconductor film and a residualarea of said second semiconductor film by radiating an energy beam witha set optimum value of energy required for crystallization; and aprocess for forming source and drain electrodes in a particular positionon said first and second semiconductor films.
 10. A process ofmanufacturing a thin film transistor according to claim 9, wherein: saidlift-off film formed in an area corresponding to said gate electrode byremoving part of said lift-off film over areas not corresponding to saidgate electrode and exposing a corresponding portion of said firstsemiconductor film using said gate electrode as a mask.
 11. A process ofmanufacturing a thin film transistor according to claim 9, wherein: saidsecond semiconductor film includes impurities.
 12. A process of a thinfilm transistor, comprising: a process for forming a gate electrode in apart on a substrate; a process for forming an insulating film on saidsubstrate and said gate electrode; a process for forming a lift-off filmin an area corresponding to said gate electrode on said insulating film;a process for forming a first semiconductor film with uniform thicknesson said lift-off film and said insulating film; a process for removingsaid lift-off film and said first semiconductor film on said lift-offfilm; a process for forming a second semiconductor film on the residualarea of said first semiconductor film and said insulating film; aprocess for crystallizing said first and second semiconductor films byradiating an energy beam; and a process for forming source and drainelectrodes in a predetermined position on said first and secondsemiconductor films.
 13. A process of a thin film transistor accordingto claim 12, wherein: said lift-off film is formed in an areacorresponding to said gate electrode by exposing from the side of saidsubstrate using said gate electrode as a mask.
 14. A process of a thinfilm transistor according to claim 12, wherein: said first semiconductorfilm includes impurities.
 15. A method of manufacturing a semiconductordevice, comprising: a process for selectively forming a metallic film ona substrate; a process for forming an insulating film on said substrate;a process for forming a semiconductor film on said insulating film; anda process for crystallizing said semiconductor film by radiating anenergy beam on said semiconductor film, wherein: the thickness of saidsemiconductor film in an area over said metallic film and that in anarea in which said metallic film is not formed are selected so that themaximum temperature in the respective areas when said energy beam isradiated is substantially equal.